Remove time_t from FFI APIs

As per rust-lang/libc#1848, we can't safely do this since the definition
of time_t depends on which version of Musl you're using on 32-bit
systems (the "time64" update for Musl 1.2), and this actually started
biting us on the arm-unknown-linux-musleabihf cross build.
Unfortunately, ISO C makes virtually no guarantees about what time_t is,
so I don't see a practical way to handle the different possibilities
robustly. We'll just cast from i64 or u64 to time_t in C and hope for
the best.

crates/bridge_core/src/lib.rs

@@ -589,7 +589,7 @@ impl<'a> CoreBridgeState<'a> {
         }
     }
 
-    fn input_get_mtime(&mut self, handle: *mut InputHandle) -> libc::time_t {
+    fn input_get_mtime(&mut self, handle: *mut InputHandle) -> i64 {
         let rhandle: &mut InputHandle = unsafe { &mut *handle };
 
         let maybe_time = match rhandle.get_unix_mtime() {
@@ -601,7 +601,7 @@ impl<'a> CoreBridgeState<'a> {
         };
 
         if let Some(t) = maybe_time {
-            t as libc::time_t
+            t
         } else {
             1 // Intentionally make this distinguishable from the error value 0
         }
@@ -1020,10 +1020,7 @@ pub extern "C" fn ttbc_input_get_size(
 
 /// Get the modification time of a Tectonic input file.
 #[no_mangle]
-pub extern "C" fn ttbc_input_get_mtime(
-    es: &mut CoreBridgeState,
-    handle: *mut InputHandle,
-) -> libc::time_t {
+pub extern "C" fn ttbc_input_get_mtime(es: &mut CoreBridgeState, handle: *mut InputHandle) -> i64 {
     es.input_get_mtime(handle)
 }
 

crates/bridge_core/support/support.c

@@ -254,7 +254,12 @@ ttstub_input_get_size(rust_input_handle_t handle)
 time_t
 ttstub_input_get_mtime(rust_input_handle_t handle)
 {
-    return ttbc_input_get_mtime(tectonic_global_bridge_core, handle);
+    /* Due to the Musl 1.2 "time64" transition, we can't safely bridge time_t
+     * between Rust and C code. And formally, ISO C provides nearly no
+     * guarantees about what the type time_t actually is. So let's just cast and
+     * hope for the best. */
+    int64_t ti = ttbc_input_get_mtime(tectonic_global_bridge_core, handle);
+    return (time_t) ti;
 }
 
 

crates/engine_xdvipdfmx/src/lib.rs

@@ -124,7 +124,7 @@ impl XdvipdfmxEngine {
                 .build_date
                 .duration_since(SystemTime::UNIX_EPOCH)
                 .expect("invalid build date")
-                .as_secs() as libc::time_t,
+                .as_secs(),
         };
 
         let cdvi = CString::new(dvi)?;
@@ -155,7 +155,7 @@ pub mod c_api {
         pub paperspec: *const libc::c_char,
         pub enable_compression: libc::c_uchar,
         pub deterministic_tags: libc::c_uchar,
-        pub build_date: libc::time_t,
+        pub build_date: u64,
     }
 
     #[allow(improper_ctypes)] // for CoreBridgeState

crates/engine_xdvipdfmx/xdvipdfmx/dvipdfmx.c

@@ -499,6 +499,9 @@ tt_engine_xdvipdfmx_main(
     return 99;
   }
 
+  /* See ttstub_input_get_mtime() in tectonic_bridge_core about bridging time_t
+   * over FFI. */
+
   rv = dvipdfmx_main(
     pdfname,
     dviname,
@@ -509,7 +512,7 @@ tt_engine_xdvipdfmx_main(
     (bool) config->deterministic_tags,
     false, /* quiet */
     0, /* verbose */
-    config->build_date,
+    (time_t) config->build_date,
     config->paperspec
   );
 

crates/engine_xetex/src/lib.rs

@@ -228,7 +228,7 @@ impl TexEngine {
                     self.build_date
                         .duration_since(SystemTime::UNIX_EPOCH)
                         .expect("invalid build date")
-                        .as_secs() as libc::time_t,
+                        .as_secs(),
                 )
             };
 
@@ -258,7 +258,7 @@ pub mod c_api {
             api: &mut CoreBridgeState,
             dump_name: *const libc::c_char,
             input_file_name: *const libc::c_char,
-            build_date: libc::time_t,
+            build_date: u64,
         ) -> libc::c_int;
     }
 }

crates/engine_xetex/xetex/xetex-engine-interface.c

@@ -15,7 +15,7 @@ int tt_engine_xetex_main(
     ttbc_state_t *api,
     const char *dump_name,
     const char *input_file_name,
-    time_t build_date
+    uint64_t build_date
 );
 
 /* These functions aren't used within the C/C++ library, but are called
@@ -53,7 +53,7 @@ tt_engine_xetex_main(
     ttbc_state_t *api,
     const char *dump_name,
     const char *input_file_name,
-    time_t build_date
+    uint64_t build_date
 ) {
     int rv;
 
@@ -62,7 +62,9 @@ tt_engine_xetex_main(
         return HISTORY_FATAL_ERROR;
     }
 
-    rv = tt_run_engine(dump_name, input_file_name, build_date);
+    /* See ttstub_input_get_mtime() in tectonic_bridge_core about bridging time_t
+    * over FFI. */
+    rv = tt_run_engine(dump_name, input_file_name, (time_t) build_date);
     ttbc_global_engine_exit();
     return rv;
 }